High-pressure and low-pressure discharge lamps require high voltages for striking which are provided by electronic ballasts. As is generally known, discharge lamps are used in a wide temperature range, for example from −25° C. to +60° C. One problem in this case is the fact that the inductance of the lamp inductor which is generally arranged in the load circuit is temperature-dependent. Thus, the maximum magnetic flux density and therefore the inductance can fluctuate in the mentioned temperature range by up to 20%. A particular problem is the fact that the inductance is reduced as the temperature increases. Thus, the lamp inductor enters saturation earlier at higher temperatures. In the case of the mentioned reduction in the inductance by 20%, the resonant frequency of the load circuit, whose resonance is utilized for striking, increases by approximately 10%. If, therefore, the resonant frequency is approached from high frequencies, resonance and therefore the production of high currents is already achieved much earlier than at lower temperatures. This entails the risk of destruction of the switches of the inverter, which in particular are often realized as MOSFETs.
This problem has been dealt with in the prior art by the saturation limit of the lamp inductor having been selected as being very high, with the result that saturation could safely be ruled out even at high ambient temperatures. This results in the following undesirable disadvantages: firstly, an inductor which has large dimensions in terms of its saturation response requires a lot of space since a larger inductor design needs to be used given the same winding losses during normal operation. This also enlarges the housing size of the electronic ballast. Both measures increase the costs of the electronic ballast considerably.
Secondly, given the same inductor design, but with a higher saturation limit of the inductor, the power loss of the inductor or the electronic ballast increases during normal operation. This results in the necessity for a larger housing design for the electronic ballast in order that the life is not shortened as a result of the thermal loading.